The present invention relates to a microwave antenna with at least one mounting device for securing a radiating patch on the antenna. The antenna is of the kind including
a radiating patch of an electrically conductive material,
a housing of rigid material,
a dielectric plate,
an electrically conductive layer serving as a ground plane on an upper side of said dielectric plate, said conductive layer having a centrally located coupling aperture, and
a feeding network on the other, lower side of said dielectric plate for feeding microwave power to said radiating patch via said coupling aperture.
Antennas of this general kind are disclosed in e.g. WO 97/43799 (Allgon AB) and WO 99/31757 (Allgon AB). Both these known antennas operate with dual polarisation obtained by forming the coupling aperture as a pair of slots crossing each other at right angles. The latter document also discloses a double patch arrangement for dual band operation.
A practical problem, which is not dealt with in these two documents, is to provide a structure which enables a swift mounting of the dielectric plate and the associated radiating patch or patches on the antenna. For the proper operation of the antenna, the plate and the patch or patches must be secured in well-defined positions in order to meet the specified radiation characteristics. Moreover, in antennas operating with dual polarisation, it is important to maintain an effective isolation between the two separate channels.
The main object of the present invention is to provide a microwave antenna with a simple mounting device, which permits an easy and quick assembly of the antenna and which secures the various components, in particular the dielectric plate and the radiating patch, in well defined positions.
This main object is achieved for an antenna having the features defined in claim 1. Accordingly, the patch and the dielectric plate have mutually aligned holes located centrally in the patch and in the plate, respectively, and the mounting device comprises a mounting column, which is secured to the housing at its lower end. The column extends centrally through the coupling aperture of the ground plane layer and in alignment with the mutually aligned holes of the patch and the plate. The column is secured to the patch at its upper end. In this way the patch and the plate are held in well-defined positions in relation to the housing and at a mutual distance from each other.
With such a structure, the mounting operation is very simple. First, the column is secured to or formed integrally with the housing at a central location, so as to stand upright thereon. Then, the dielectric plate with the feeding network and the ground plane layer is threaded onto the column, whereupon the patch is secured to the top of the column by means of a fastening screw. Alternatively, the mounting column may be formed as a relatively long screw extending through the holes of the patch and the plate and being in threaded engagement with the housing at its lower end.
The patch is preferably held at a distance from the plate by means of spacing elements defining the mutual distance therebetween. In a particularly advantageous embodiment, the patch and the plate are held together by the spacing elements and are mounted as a unit onto the housing.
Preferably, the patch and the plate are clamped-together against the housing so as to be securely positioned when the patch is secured to the upper end of the mounting column.
The mounting column may extend freely through the plate and the coupling aperture, which makes it possible to locate the plate in an exact position on the housing when being clamped thereon.
It has turned out that the central column and the aligned holes in the patch and the plate do not have a negative influence on the radiation characteristics of the antenna.
These and other features will be apparent from the detailed description below and the appended claims.